Various kinds of pin or needle-type probes for use in circuit board testers are known from prior art. FIG. 6, for example, shows a prior art circuit board tester in which a predefined regular grid pattern of a grid pattern array G is translated with the aid of a pattern adapter R to the usually irregular arrangement of the test points T of a circuit board P to be tested. The pattern adapter R comprises as a rule several guide layers F spaced away from each other. Guide holes are incorporated into the guide layers F for receiving the probes N. The probes N are rigidly held in the adapter R and canted so that they can electrically connect the contact points of the regular grid pattern G to the circuit board test points T since these deviate from the regular arrangement of the base pattern.
To compensate irregularities in the arrangement of the circuit board test points T of the circuit board P to be tested and for an electrically reliable contact with the grid pattern array G, the pattern adapter R is in contact with a full pattern cassette V, which is equipped with resilient probes S in the corresponding pattern of the grid pattern array G. The full pattern cassette V has a full complement of probes while the pattern adapter R usually comprises only as many probes as the circuit board P comprises circuit board test points T to be tested. The styles of the probes N are usually rod-shaped and feature bosses or thickened ends as disclosed in, for example, by EP 0 149 776 B2 and DE G 90 14 236.5 U1.
Modern circuit boards comprise many internal wiring planes and/or are configured to directly receive highly integrated circuits (ICs). More particularly by making use of high-density terminal arrays, such as for example ball grid arrays (BGA), the requirements on the number of contact points to be contacted and sensed on a circuit board have substantially increased. At the same time the spacing between the contacts on such circuit boards has been reduced to approx. 0.25 millimeters (mm) (10 mil). For adapters in this field of application, extremely thin probes are used, having, for example, a diameter of only 0.1 mm to 0.2 mm. These probes are, therefore, extremely unstable. Many guide layers are usually required in the adapter to reliably guide them. Due to the requirements, the manufacturing of testers that are tailored to each style of circuit board to be tested has become very complicated.
Disclosed in the article xe2x80x9cSMD technology changes test equipmentxe2x80x9d in xe2x80x9cFeinwerktechnik and Messtechnikxe2x80x9d (Precision Mechanics and Metrology)98, No. 7/8, pages 317-318 is a contact probe for SMD-populated circuit boards, which has a probe sleeve and a plunger capable of sliding in the probe sleeve. The diameter of the plunger is 1.3 mm. The article describes probes with probe sleeves having a low wall thicknesses and with plungers of smaller shank diameter as disadvantageous.
U.S. Pat. No. 4,896,107 shows contact probes with conically tapering tips. In the shank area, these contact probes have a maximum thickness of 1.3-1.4 mm, while the head formed on the contact probe has a diameter of 2 mm.
DE 36 43 305 A1 shows a spring contact probe with an elongated metal cylinder serving as a sleeve, and a one-piece metal tube-screw-spring component, which is inserted in the sleeve to form a contact probe capable of sliding in the sleeve.
Another contact probe is disclosed by DE 34 26 295 A1. This contact probe in turn has a sleeve and a plunger. The plunger is provided with a flattened section against which a crimped slot of the sleeve engages. The provision of such a contour shows that the plunger used here is relatively thick.
U.S. Pat. No. 4,633,176 relates to an adapter for the testing of circuit boards provided with test probes capable of swiveling outwards. The latter are swiveled out and aligned with predetermined contact points on the circuit board to be tested by means of a conical tip and holes acting in conjunction with the conical tip.
In accordance with the invention, a circuit board tester probe comprises a needle and a sleeve, the needle being shiftingly guided in the sleeve and the needle protruding at least 10 mm from the sleeve, and preferably more than 20 mm. The needle tapers gradually and conically to a contact tip at the area projecting from the sleeve.
This projecting, gradually and conically tapering area of the contact tip permits very dense positioning of the contact probes in the area of their contact tips, since in this area the contact probe has a very small thickness because of the conically tapering tip.
Due to the needle being guided in the sleeve, an improved inherent stiffness of the probe is achieved with resilient compensation thereof at the same time. In addition, a probe in accordance with the invention is easy to integrate in adapters for strobing high-density contact arrays having little spacing between the contact surfaces.
This combination of a needle gradually tapering to a contact tip and a sleeve from which a considerable portion of the needle projects, thus permits a dense array of several test probes in the area of their contact tips. It also has the necessary rigidity and is simple in design.
Furthermore, an adapter in accordance with the invention comprises at least two layers in parallel in which resilient probes of the aforementioned kind are mounted in through-holes. The probes are arranged partly canting and with protruding contact tips for contacting a test object. The probes on a side of the adapter opposite the test object are configured for contacting a grid pattern array with a regular arrangement of contacts.
The adapter in accordance with the invention thus eliminates a split arrangement into a full pattern cassette with resilient probes and a rigid needle adapter for adapting a regular pattern as usual with grid pattern arrays to an optional pattern of a test object. In this case, the sleeve handles the substantially supporting and guiding functions so that the number of inner layers can be minimized. In adapters, the hole pattern of each layer needs to be computed by the computer and machined with a drilled hole pattern by high-precision CNC machine tools so that each layer saved makes for considerable cost savings while significantly reducing inventory requirements.
Furthermore, a circuit board tester in accordance with the invention is characterized by a configuration including a regular grid pattern array. An adapter includes several probes, the adapter comprising at a first upper side contacts in electrical contact with the probes, which are adapted to a contact arrangement on the test array, and the contact tips of the probes protruding from a second upper side, whereby each of the contact tips is assigned to a specific circuit board test point of a test object and is in electrical contact with the circuit board test point of a test object inserted in the tester. This tester is configured of the components in accordance with the invention as described above and provides all of the cited advantages as a closed system.
The above and other features of the invention including various novel details of construction and combinations of parts, and other advantages, will now be more particularly described with reference to the accompanying drawings and pointed out in the claims. It will be understood that the particular method and device embodying the invention are shown by way of illustration and not as a limitation of the invention. The principles and features of this invention may be employed in various and numerous embodiments without departing from the scope of the invention.